Circuit boards, semiconductor devices, and various displays have a patterning layer such as a wiring layer or an electrode layer, which is made of metal such as copper, nickel or silver. In particular, a patterning layer using copper is widely used due to good electric conductivity and low price.
Particularly, copper particles and copper oxide particles such as cuprous oxide may be produced with small diameter in a several nanometer or several micrometer level such that they may form a fine pattern, so they are useful in forming an electroconductive copper patterning layer.
Seeing conventional methods for forming an electroconductive copper patterning layer using copper-based particles, a paste mainly containing copper-based particles is printed on a substrate surface or filled in through holes of the substrate to form a copper-based particle patterning layer, and then the layer is thermally treated at a high temperature under the inert gas circumstance for burning. Accordingly, among the copper-based particles contained in the copper-based particle patterning layer, copper oxides are reduced into copper and thus connected with each other, and organic substances included in the paste are removed, so an electroconductive copper patterning layer is formed (see Japanese Laid-open Patent Publication No. 2006-93003).
This burning method gives a copper patterning layer with good electric conductivity to some extent, but it is not easy to adopt the burning process under an inert gas circumstance in the industrial aspect. On the while, in case a burning process under a common atmospheric circumstance, copper may be oxidized, which results in bad quality of electric conductivity of the formed copper patterning layer.